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Efficient CO2 storage in aquifers is often hindered by early gas breakthrough, prolonged drying times, and permeability decrease induced by salt precipitation and/or fines migration—particularly in clay-rich sandstone formations. This study investigates the use of alternating nitrogen (N2) injection as a pre-treatment method to enhance CO2 storage performance. Coreflooding experiments were conducted on high kaolinite-content Berea sandstone cores, comparing drying efficiency, breakthrough timing, formation damage and fines production during N2 and CO2 injections. Results showed that N2 achieved drying stabilization after approximately 7,000 pore volumes injected (PVI), compared to 12,000 PVI for CO2. N2 injection also resulted in delayed gas breakthrough and faster water displacement. Although CO2’s lower vapor humidity slowed evaporation, fines migration during its injection redistributed gas flow paths and partially enhanced drying. Nevertheless, CO2 caused more severe permeability damage, with a 1.64-fold reduction compared to only 1.08-fold for N2. These findings demonstrate that N2 pre-injection improves drying efficiency and mitigates injectivity decline, supporting its use as cushion gas for CO2 storage operations.